Honeywell PRIMUS 660 Pilot's Manual page 143

R
PRIMUS 660 Digital Weather Radar System
The National Weather Service (NWS) radar observer is able to
objectively determine storm intensity levels with VIP equipment. These
radar echo intensity levels are on a scale of one to six. If the maximum
VIP levels are 1 "weak" and 2 "moderate," then light to moderate
turbulence is possible with lightning. VIP Level 3 is strong and severe
turbulence is possible with lightning. VIP Level 4 is very strong and
severe turbulence is likely with lightning. VIP Level 5 is intense with
severe turbulence, lightning, hail likely, and organized surface wind
gusts. VIP Level 6 is extreme with severe turbulence, lightning, large
hail, extensive wind gusts, and turbulence.
Thunderstorms build and dissipate rapidly. Therefore, do not attempt
to plan a course between echoes. The best use of ground radar
information is to isolate general areas and coverage of echoes. You
must avoid individual storms from in–flight observations either by visual
sighting or by airborne radar. It is better to avoid the whole thunderstorm
area than to detour around individual storms unless they are scattered.
Airborne weather avoidance radar is, as its name implies, for avoiding
severe weather – not for penetrating it. Whether to fly into an area of
radar echoes depends on echo intensity, spacing between the echoes,
and the capabilities of you and your aircraft. Remember that weather
radar detects only precipitation drops; it does not detect turbulence.
Therefore, the radar scope provides no assurance of avoidance
turbulence. The radar scope also does not provide assurance of
avoiding instrument weather from clouds and fog. Your scope may be
clear between intense echoes; this clear does not mean you can fly.
Remember that while hail always gives a radar echo, it may fall several
miles from the nearest cloud and hazardous turbulence may extend to
as much as 20 miles from the echo edge. Avoid intense or extreme level
echoes by at least 20 miles; that is, such echoes should be separated
by at least 40 miles before you fly between them. With weaker echoes
you can reduce the distance by which you avoid them.
DO'S AND DON'TS OF THUNDERSTORM FLYING
Above all, remember this: Never regard any thunderstorm lightly even
when radar observers report the echoes are of light intensity. Avoiding
thunderstorms is the best policy. Following are some do's and don'ts of
thunderstorm avoidance:
D
Don't land or take off in the face of an approaching thunderstorm.
A sudden gust front of low level turbulence could cause loss of
control.
Federal Aviation Administration (FAA) Advisory Circulars
A–8
A28–1146–111
REV 2